Aluminum alloy



UNITED STATES PATENT OFFICE ALUIVIIN'UM ALLOY Ludwig J. Weber, New Kensington, Pa., assignor to Aluminum Company of America, Pittsburgh, Pa., a corporation of Pennsylvania No Drawing. Original application September 21, 1932, Serial No. 634,150. Divided and this ap-' plication November 30, 1932. Serial No. 645,131

3 Claims. (Cl. 75-1) This invention relates to aluminum base alloys in the alloys which are herein described and containing magnesium and zinc and to the imwhich are the subject of the present invention, provement of such alloys by the addition thereto the copper must be added in amounts of 0.5 to of certain alloying elements. 2.5 per cent before the tendency of the alloys to 5 The alloys to which this invention refers and stress crack is materially reduced. With less which it is the general object of this invention than 0.5 per cent of copper no appreciable efiect to improve are those aluminum base alloys which is had while when the amount of copper exceeds contain at least '75 per cent by weight of alumi about 2.5 per cent by weight, the other material num, '7 to 15 per cent by weight of zinc, and properties of the alloy, such as workability, due- 10 0.2 to 2.5 per cent by weight of magnesium. tility, etc., are so materially affected as to pre- The detrimental properties hereinafter described elude, as I have found, further additions. It is an and which this invention is designed to correct important property of these aluminum base alloys will be found in such alloys whether or not they containing 75 per cent aluminum, 7.0 to 15.0 per contain other alloying elements, such as are cent of zinc, and 0.2 to 2.5 per cent of magnesium,

added to aluminum base magnesium alloys to that the addition of 0.5 to 2.5 per cent of copper produce a property in or modify an old property thereto does not materially increase the susof the alloy. ceptibility of the alloy to the pitting type of This application is a division of my copending corrosion, whereas to the aluminum base alloys application Serial No. 634,150. containing 5 to 15 per cent of magnesium there "20 It is characteristic of these alloys that where cannot be added copper in amount much greater the alloy is under high stress, either external than 0.20 per cent lest the pitting type of coror internal in source, and is exposed to a corrosion be increased. Yet in such case, as I have rosive condition, as for instance corrosive soludiscovered, the tendency of the alloys to stress tions, gases, etc., a peculiar cracking or struccrack is greatly lessened.

V 25 tural failure may occur. This phenomenon is In addition to the elements specifically named herein designated as stress cracking. The as being present in my improved alloys, the alstress cracking of aluminum base alloys containloys may contain other alloying elements which ing zinc and magnesium in the proportions above may be added to produce some particular propmentioned does not occur under all conditions or erty. The presence or absence of these alloying 30 at all times under usual service conditions and, elements does not affect the results obtained by in fact, its occurrence may be rare. However, my invention since the tendency to stress crackthese alloys are valuable as a high strength coning is due to the presence of the magnesium and struotion material and any failure at all is serious. zinc and is diminished by the presence of the The elimination or diminution of stress crackcopper. One alloying element which has a very I ing inthese alloys is of great importance and parbeneficial effect on my alloys is manganese. I ticularly is it of importance to so modify the have discovered that in the presence of 0.1 to 1.5 alloys that the possibility of stress cracking under per cent of manganese the addition of the 0.5 to ordinary service conditions will be largely elim- 2.5 per cent by weight of copper has a greater inated. It is to this end that the present inveneffect in suppressing the tendency of the alloy to i 40 tion is directed. stress crack 50 alloys, however, the copper did not prevent said comprises melting the aluminum and adding the As was described in my copending application Although any good commercial grade of alumifor United States patent, Serial No. 634,149, filed num may be used successfully in making the Sept. 21, 1932, the addition of a certain amount alloys, I have found that the alloys are least of copper to aluminum base alloys containing prone to stress cracking when the aluminum used 5 to 15 per cent by weight of magnesium tended in their fabrication is of relatively high purity to diminish stress cracking under ordinary servand contains 99.6 per cent or more of aluminum. ice conditions, these said aluminum-magnesium I prefer, consequently, to use metal of such high alloys being also subject to this phenomenon of purity. The alloys may be manufactured by any stress cracking. When zinc was added to 'su'clr convenient method, the most common of which stress cracking. Now I have determined that alloying elements thereto in the desired proporcopper will in the case of certain of the aluminum tions.

base alloys containing magnesium and zinc pro- Of the alloys to which this invention pertains, duce this desired effect but only when the copper there are certain which are found to be extremely is present in certain amount. That is to sayuseful in the industry as structural materials and no which excel in strength and resistance to corrosion. One of such alloys contains 9 to 11 per cent by weight of zinc, 0.3 to 0.6 per cent by weight of magnesium, 0.6 to 0.9 per cent by weight of manganese, and 0.9 to 1.1 per cent by weight of copper. This alloy has, in the worked, heat-treated and aged condition, an average tensile strength of about 66,000 pounds per square inch, a yield point of about 56,000 pounds per square inch, and an elongation of about 16.3 per cent in 2 inches. The alloy is therefore an excellent structural material. Another excellent alloy is one containing 10 per cent by weight of zinc, 2 per cent by weight of magnesium, 2 per cent by weight of copper, and 1 per cent by weight of manganese. This alloy, in the worked heattreated and artificially aged condition, has a tensile strength of about 90,000 pounds per square inch, a yield point of about 86,000 pounds per square inch, and an elongation of 6 per cent in 2 inches. In both of these alloys the tendency to stress cracking has been substantially relieved by the addition thereto of the amount of copper mentioned.

As above indicated, the alloys of the present invention may be heat-treated, aged and/or otherwise thermally treated by the methods known to the art to materially improve or change their physical properties. One of the unusual properties of my novel a loys is that when the alloys are heat-treated, cooled and subsequently artificially aged by heating the alloy, according to usual practice, to temperatures of 100 to 200 centigrade, the susceptibility of the alloy to intercrystalline corrosion is materially lessened. This is in contradistinction to all other heat-treatable aluminum base alloys known since artificial aging has heretofore increased rather than decreased the susceptibility of the alloys to intercrystalline corrosion.

I claim:

1. A metallic alloy consisting of 7.0 to 15.0 per cent by weight of zinc, 0.1 to 1.5 per cent by weight of manganese, 0.2 to 2.5 per cent by weight of magnesium, and 0.5 to 2.5 per cent by weight of copper, the balance being substantially aluminum.

2. A metallic alloy consisting of 9.0 to 11.0 per cent by weight of zinc, 0.3 to 0.6 per cent by weight of magnesium, 0.6 to 0.9 per cent by weight of manganese, and 0.9 to. 1.1 per cent by weight 01 copper, the balance being substantially I aluminum. 

